This invention relates to optoelectronic devices and more particularly to light emitting devices fabricated from a semiconductor material, such as silicon, and a method of fabricating such a device.
Light emitting devices fabricated from silicon are known in the art. One such a device is a two junction device having a sandwiched configuration of immediately adjacent doped p+np+ or n+pn+ regions. The device comprises a first pn junction which is reverse biased into a breakdown mode, to emit light and a neighbouring second pn junction which is forward biased to inject carriers into the first junction, thereby to improve the internal quantum efficiency of the device. It is also known to drive the device into a punch-through mode wherein a depletion region associated with the reverse biased junction punches through to a depletion region associated with the forward biased junction, thereby to lower an energy barrier of the forward biased junction and facilitate the injection of carriers from the forward biased junction into the reverse biased junction and to improve electroluminescence effects in the device.
Another known light emitting device has a sandwiched configuration of immediately adjacent doped n+pp+ or p+nn+ regions. The device comprises a first pn junction, which is reverse biased into a breakdown mode to emit light and a neighbouring pp+ or nn+ junction. In use, the device may be driven into a reach-through mode, in that the depletion region of the reverse biased junction reaches through the p region to the p+ region or through the n region to the n+ region, as the case may be, before the reverse biased junction reaches breakdown, thereby to improve electroluminescence effects in the device.
In modern standard bulk CMOS, including BiCMOS, fabrication processes, more particularly sub-micron processes, lateral device isolation techniques, such as local oxidation of silicon (LOCOS) and/or shallow trench isolation (STI), are used to form physical isolation structures or barriers comprising bodies of an isolating material for laterally isolating from one another doped implanted n+ or p+ active regions for forming junctions with a p- or n-type bulk substrate material. These techniques, by necessity, cause the barriers to be formed between mutually facing faces of the implanted active regions. These barriers between the doped active regions would inhibit the aforementioned punch-through and reach-through modes.
In other known devices, a gate structure is formed between implanted regions, which structure inhibits transmission of emitted light transversely and outwardly from the device.